The impact of Coronavirus Nsp1 on host mRNA degradation is independent of its role in translation inhibition.

When host cells are infected with coronaviruses, the first viral protein produced is non-structural protein 1 (Nsp1). This protein inhibits host protein synthesis and induces host mRNA degradation to enhance viral proliferation. Despite its critical role, the mechanism by which Nsp1 mediates cellular mRNA degradation remains unclear. In this study, we use cell-free translation to address how host mRNA stability is regulated by Nsp1. We reveal that SARS-CoV-2 Nsp1 binding to the ribosome is enough to trigger mRNA degradation independently of ribosome collisions or active translation. MERS-CoV Nsp1 inhibits translation without triggering degradation, highlighting mechanistic differences between the two Nsp1 counterparts. Nsp1 and viral mRNAs appear to co-evolve, rendering viral mRNAs immune to Nsp1-mediated degradation in SARS-CoV-2, MERS-CoV, and Bat-Hp viruses. By providing insights into the mode of action of Nsp1, our study helps to understand the biology of Nsp1 better and find strategies for therapeutic targeting against coronaviral infections.